Radar systems have conventionally been used to detect objects for various purposes. Radar systems have been applied to commercial and military aviation and in other vehicular systems. Radar systems have also been used in military systems and have been proposed for use in collision avoidance systems for passenger automobiles.
One type of radar system, a two-tone continuous wave radar system, is described in U.S. Pat. No. 5,402,129 by Robert C. Gellner et al. This patent describes a vehicular tracking system that uses a dual lobe, monopulse antenna to transmit a narrow beam radar signal at a vehicle. The reflected signal is received by the two lobes and both a sum signal and a difference signal are generated. The sum and difference signals are then processed to determine the angle of a target relative to the received signal.
Another type of radar system is described in patent applications entitled “Method and Apparatus For Correcting Velocity-Induced Range Estimate Phase Errors in a Two-Tone Monopulse CW Radar,” by Paul Fiore and Eric Rundquist, filed on Oct. 1, 2004, and assigned Ser. No. 10/956,837; and “Method and Apparatus For Improved Determination of Range and Angle of Arrival Utilizing a Two-Tone CW Radar,” by Paul Fiore, filed on Oct. 1, 2004, and assigned Ser. No. 10/956,643. These applications describe the use of a two-tone, continuous wave radar system for use in tracking rocket propelled grenades (RPGs). These radar systems also use sum and difference signals to determine an angle of the target relative to a reference direction.
In general, radar designs vary widely, ranging from low-cost continuous-wave (CW) systems, to high performance, pulse-Doppler and synthetic aperture approaches. For a radar to measure range, it is typically thought that some form of amplitude or phase modulation of the carrier is required. However, there is a method using more than one CW signal that can in fact provide range. A device known as a “tellurometer” is available for geodetic survey work, and makes use of the fact that the survey equipment is not moving (i.e. zero Doppler shift).
Radar designs also are used for the case where a target is expected to have a velocity. The utilization of multiple CW transmitted signals can produce the estimates of range, and to distinguish whether a target is approaching or receding. Another measurement that radars are often required to make is that of the two-dimensional (azimuth/elevation) direction of arrival (DOA) of the target. A basic approach is to use multiple antennas in a phased-array configuration for this determination. When multiple tone/multiple channel radar systems are implemented, a plurality of data streams are produced. In prior radar systems, the calculation of range and DOA are performed as separate, independent functions.
There remains a need, however, for a system to quickly and accurately determine the range, relative angle and velocity of a target from a point of reference. There is a further need for such a technique to be implemented relatively cost effectively, and in an environment where the data may be “noisy.”